DE60202373T2 - PROCESS FOR THE PREPARATION OF LITHIUM TITANATE - Google Patents

Abstract

A process is provided for making lithium titanate of closely controlled particle size in the range 5 nm to 2000 nm. The process includes re-firing lithium titanate under controlled conditions so that crystallites of the desired particle size are grown. The lithium titanate may be derived from any suitable source. A suitable source of lithium titanate can be from a process that includes evaporation of a blend that contains lithium and titanium to form a mixture containing lithium and titanium compounds that are subsequently calcined to form lithium titanate. The blend of titanium and lithium may be derived from a variety of titanium and lithium precursor materials.

Description

The Invention claims the priority of U.S. Pat. No. 60 / 306,683.

The present invention relates to a process for producing lithium titanate, parts of the process and the product of the process. More particularly, the present invention relates to a process for producing tetra-lithium titanate spinel particles having a well-controlled particle size in the range of 5 to 2,000 nm and which correspond to the stoichiometric formula Li ₄ Ti ₅ O ₁₂ . The lithium titanate may be from any suitable source. An object of the present invention relates to a process for producing the lithium titanate.

BACKGROUND THE INVENTION

Lithium titanates are materials that are developed for the electrodes of lithium-ion batteries. The crystal form Li ₄ Ti ₅ O ₁₂ (spinel) is in particular the preferred form for secondary (rechargeable) batteries, due to the preferred incorporation properties.

There are several known methods for preparing lithium titanate, and in particular Li ₄ Ti ₅ O ₁₂ spinel. For example, US Pat. No. 5,545,468 teaches a process for preparing lithium titanate by reacting titanium dioxide in the anastase or rutile form with lithium carbonate or hydroxide in the range of 700 ° C to 1,000 ° C.

In recent years, it has become clear that a smaller particle size in the electrode material generally allows a faster charging speed of the lithium-ion battery and a larger number of charging cycles without deterioration. Japanese Patent Application 09-309727 teaches a method for producing lithium titanate structures from long particles containing many voids having a longest dimension of 0.1 to 50 μm and a specific surface area of 1-300 m ² / g. The particles are prepared by reacting a titanium and a lithium compound in solution, precipitating with ammonia, drying and calcining.

The Japanese Patent Application 2000-302547 teaches a method of production Lithium titanates by calcining a mixture of a Titanium and a lithium compound followed by a multistage Erwännungs- and cooling program. The proposed method is intended to provide improved phase control and provide reduced loss of lithium compared with the U.S. 5,545,468. Supposedly, it also provides a cheaper processing without wastewater treatment problems available with JP 09-309727 are connected. However, it does not relate to the subject of crystal size or the specific surface.

Peramunage et al., Preparation and Battery Applications of Micron sized Li ₄ Ti ₅ O ₁₂ , Mat. Res. Soc. Symp. Proc., Vol. 498, No. 496, pp. 359-365 (1998) and Peramunage et al. Preparation of Micron-Sized Li ₄ Ti ₅ O ₁₂ and its Electrochemistry in Polyacrylonitrile Electrolyte-Based Lithium Cells, J. Electrochem. Soc., Vol. 145, No. 8, pages 2609-2,615 (August 1998) describes the preparation of micron size Li ₄ Ti ₄ O ₁₂ using a one-step solid state reaction.

PCT WO 02/46101 describes a process for the synthesis of lithium-titanium structures, which can be coated with carbon for electrochemical properties provide.

SUMMARY THE INVENTION

The present invention provides a process for economically producing lithium titanate crystallines and in industrial grades. The method achieves good phase and size control in the range of 5 to 2000 nm (comprised between 10 to 2000 nm) and a BET surface area in the range of 1 to 400 m ² / g. In general, the method comprises providing a source of lithium titanate, grinding the lithium titanate to a particle size smaller than the desired particle size, and re-firing the lithium titanate under conditions to form a final lithium titanate having a desired particle size produce narrow size distribution and controlled surface.

In An object of the method is the lithium titanate by a A method comprising forming a mixture, which includes titanium and lithium. The evaporation is at a Temperature above the boiling point of the liquid carried out in the mixture, however below the temperature at which a significant reaction the lithium and the titanium compound occurs. The mixture will calcined to form lithium titanate. The calcined product can be washed to remove traces of soluble salts.

The Lithium titanate is ground or crushed to a size which the desired size of the final product is equal to or less than this. The ground or ground Lithium titanate is spray-dried. Optionally, the crushed lithium titanate may be re-fired under conditions of lithium titanate with a desired surface and size distribution to create.

The Mixture of titanium and lithium can be made of a variety of suitable Sources are provided. Consequently, according to a Subject of the invention, the mixture of titanium and lithium as aqueous chloride solutions made of titanium and lithium. In a second item invention, the mixture of titanium and lithium as a suspension an amorphous oxidized titanium compound in a lithium solution. In this case, the lithium solution from a source of lithium, selected from the group consisting of lithium hydroxide, lithium chloride, lithium nitrate, Lithium sulfate, lithium fluoride, lithium bromide, lithium oxide and their Mixtures.

In A third aspect of the invention is lithium titanate by known means and grinding to a particle size which is smaller is as the particle size of the final product, as the source of lithium and titanium for the re-firing step used, in which the crystals grow to the desired size.

As The following description and the appended claims all refer to Percentages by weight unless otherwise specified.

SHORT DESCRIPTION THE DRAWINGS

1 shows a flowchart of a general subject of the method according to an embodiment of the invention.

2 FIG. 10 shows a flow chart of the process according to another embodiment of the present invention wherein the titanium source is a titanium oxychloride solution and the lithium source is lithium chloride.

3 FIG. 10 shows a flowchart of the process according to another embodiment of the present invention wherein the titanium source is an amorphous oxidized titanium compound and the lithium source is lithium hydroxide or a lithium salt.

4 Figure 12 shows a flow chart of the process according to the present invention wherein lithium titanate, prepared by known means, is ground to a size smaller than the required size and subjected to a re-firing step and subsequently dispersed.

5 shows a scanning electron image of the product of the method after the calcination step 30 ,

6 shows a scanning electron micrograph of the product of the process after grinding, drying and re-firing at 700 ° C, ie after step 50 ,

DESCRIPTION THE INVENTION

The The present invention relates to a process for economical Production of lithium titanate with good phase and size control made of lithium titanate, in industrial qualities. The lithium titanate can be provided by a method which is hereafter or any suitable lithium titanate source.

According to one Subject of the present invention is the lithium titanate according to the following Process produced. A mixture is provided which Includes titanium and lithium. The mixture is evaporated to particles to form a mixture of lithium and titanium compounds contain. The evaporation is at a temperature above the Boiling point of the liquid carried out in the mixture, but below the temperature at which significant reactions the lithium and titanium compounds occur, or in which the Crystallization of lithium titanate occurs. The particles will be calcined to form lithium titanate.

The lithium titanate is ground or ground to a size smaller than or equal to the desired size of the final product. Subsequently, the material is spray-dried so that the spray-dried product, Li ₄ Ti ₅ O ₁₂ , can be used as is, or micronized to form a micronized Li ₄ Ti ₅ O ₁₂ end product be burned again. Typically, the milled lithium titanate is again fired under conditions to produce lithium titanate having a desired surface area and particle size.

Referring to 1 , a flow chart according to the general method is shown. According to the present method, a titanium source is connected to a lithium source to form a mixture 10 to build. The titanium source can be derived from any suitable precursor, as will be explained later. Similarly, the lithium source can be derived from any suitable precursor, as explained below.

The mixture is placed in a device 20 evaporates to achieve complete or near complete evaporation. In other words, the solution is vaporized to form particles so that less than about 5 to 20% of water remains. The particles are calcined 30 to form lithium titanate particles. Preferably, the lithium titanate particles are present in a thin layer.

After calcining, the particles can be in water 35 be washed to remove all traces of soluble salts from the product of the calcination step.

The particles are ground to a desired mean size and particle distribution 40 , After milling, the particles are spray dried 45 in a spray dryer at a temperature of about 120 ° C to about 350 ° C, preferably between about 200 ° C to about 250 ° C. After spray-drying, the lithium titanate is normally fired again in a controlled temperature oven 50 to produce particles having a desired surface area and particle distribution. The product from the re-firing step consists of thermally treated agglomerates or aggregates. Alternatively, the spray-dried particles may be used as is or micronization 47 to reduce the particle size to a desired particle size between 5 and 2,000 nm (including between 10 to 2,000 nm).

When the lithium titanate is re-fired, the aggregates produced from the re-firing can then be placed in a wet mill 60 be dispersed or can be micronized 90 , When the particles are dispersed, they may be further processed or left as they are, ie, as a slurry. Further processing can be spray-drying 80 to produce spray-dried powder agglomerates consisting of primary particles. The spray-dried powder agglomerates can be sold or can be further processed by micronizing 90 to produce a fully dispersed powder.

The Specific steps of the procedure are detailed below explained.

Lithium-titanium mixture

As mentioned above, a mixture of titanium and lithium is provided by a Lithium source and a titanium source is provided. This mixture can be referred to herein as the lithium-titanium mixture or the titanium-lithium mixture be designated.

For example, in one embodiment of the present invention, as in 2 shown, the mixture of titanium and lithium, a lithium-titanium solution 110 , which can be prepared by connecting an aqueous solution of titanium with an aqueous lithium source. In particular, an aqueous titanium chloride solution is combined with an aqueous lithium chloride solution. The aqueous titanium chloride solution can be prepared by introducing water-free titanium chloride in water or in a hydrochloric acid solution.

The wässrge Titanium chloride solution can also be derived from the processing of titanium ores with hydrochloric acid become. For example, it may result from the processing of titanium ore according to U.S. Pat. Patent No. 6,375,923, the entire contents of which are hereby incorporated by reference is included.

A aqueous solution Lithium chloride can be obtained by adding lithium chloride or oxychloride dissolved in water will or by dissolving a lithium compound such as lithium carbonate or lithium hydroxide in a hydrochloric acid solution. These For example, lithium compound can be dissolved in the acidic titanium chloride solution, which is formed as a first step.

In another embodiment of the present invention, as in 3 shown, is the mixture of titanium and lithium 210 a suspension of an amorphous oxidized titanium compound in a lithium solution. The titanium compound may be prepared by any means including precipitation from a titanium salt solution by addition of a hydroxide. It may also be prepared using the intermediate of the process described in US Patent No. 09 / 503,365 or the process described in US Patent No. 09 / 503,636, the entire contents of which are incorporated herein by reference. The intermediate to be used in the present process is a hydrolysis product prior to the calcination step described in the applications incorporated by reference above.

In These applications, the intermediate product is formed by a Titanium salt in an aqueous solution along with optionally smaller amounts each of a variety of converted into an oxidized titanium solid by chemical control agents, in a process involving the entire, controlled evaporation the solution and forming an amorphous titanium compound. The evaporation process is carried out above the boiling point of the solution and below the temperature at which significant crystal growth occurs.

The lithium for this embodiment of the present invention may be provided as lithium nitrate, lithium chloride, lithium carbonate, lithium hydroxide, lithium sulfate, lithium oxide, lithium fluoride, lithium bromide or other soluble lithium compounds or their mixture. In yet another embodiment, as in 4 As shown, the lithium and titanium are provided as lithium titanate. The lithium titanate may be from any suitable process. In this embodiment, the lithium titanate feedstock is a cerium are subjected to a particle size smaller than the particle size of the desired product, and further subjected to firing and dispersing.

The ratio of the titanium to the lithium in the mixture is adjusted to correspond to or slightly less than the Ti to Li ratio of the desired lithium titanium compound. To produce the preferred lithium titanate spinel, Li ₄ Ti ₅ O ₁₂ , the ratio of the amount of Li to the amount of Ti (Li / Li) corresponds to the stoichiometry of 0.116. A slight excess of Li over the stoichiometric amount, e.g. B. up to 10% more than the stoichiometric amount, ie up to a weight ratio Li / Ti ratio of 0.128, can be added to account for the volatilization of the Li salt during processing. It is possible to achieve 98% or better Li ₄ Ti ₅ O ₁₂ phase purity.

One Method of achieving good phase purity is to begin by mixing a mixture of lithium and titanium compounds with a Li / Ti relationship of 0.116, take a small sample of this To dry and calcine, the phase purity of the sample through X-ray diffraction to measure and use this result to the Li / Ti ratio like required to adjust.

With respect to in 2 In the illustrated embodiment, the concentrations of titanium in the solution can vary over a wide range, but are generally in the range of 30 to 150 g / l Ti. Higher titanium concentration is generally more economical. With respect to in 3 In the illustrated embodiment, the amount of the titanium compound in suspension is generally in the range of 20% to 60% by weight.

Evaporation process

After this the mixture of lithium and titanium was produced, becomes the mixture evaporated (20, 120, 220). The evaporation process is above the boiling point of the liquid carried out in the mixture and below the temperature at which significant reactions occur the lithium and titanium compounds, or in which a considerable Crystallization of lithium titanate appearance. As a result of the Evaporation, become water and acid (eg hydrochloric acid, Nitric acid, nitrous acid) evaporated and can be recovered by any suitable method.

The Evaporation process is carried out in a way to to control the physical form of the product. Preferably The evaporation process is carried out by spraying the mixture while it is is heated to a temperature in the range of about 120 ° C to about 350 ° C, and more preferably in the range of about 200 ° C to about 250 ° C. This Method can be used in a spray dryer carried out become.

With respect to in 2 As shown, the evaporation process is carried out in such a manner as to form a layer of a mixture of a lithium compound and an amorphous oxidized titanium compound. With respect to in 3 As shown, the evaporation method is performed so as to form a thin layer of a lithium salt on pre-existing particles of an amorphous oxidized titanium compound.

In both cases, by controlling the operating parameters, including the temperature and concentration of titanium and lithium, the properties of the solid intermediate can be reliably controlled within a very narrow range. For example, the products resulting from injection in a spray dryer according to the in 2 shown embodiment, generally consist of hollow balls or parts of balls. The dimensions of the spheres may vary from less than 0.1 μm to 100 μm or more in diameter and a shell thickness ranging from about 30 nm to about 1000 nm or more. The structure of the sleeve consists of an intimate mixture of titanium and lithium compounds.

The Evaporation by spraying under the conditions of the invention also has the advantage of direct processing of the solution, so that a homogeneous intermediate is formed and so that the evaporation of water and acid performed simultaneously becomes. Preferably, approximately between 90% to about 99% of any aqueous material evaporated.

calcination

The product resulting from the evaporation step is calcined (30, 130, 230) at a temperature and for a time sufficient to convert the mixture of titanium and lithium compounds to lithium titanate having the desired structure and particle size. The calcining temperatures may range between about 600 ° C to 900 ° C. Preferably, calcination is conducted at temperatures in the range of about 700 ° C to about 900 ° C. The calcination time varies over a wide range, from about 1 hour to as long as 36 hours. Preferably, the calcination time is in the range of about 6 hours until about 12 hours. Lower temperatures require longer calcination times. The product of calcination shows a structure of individual units which can be broken up by grinding into particles of a desired mean size and size distribution.

During the Calcining, the lithium salt reacts with oxygen and water in the furnace atmosphere, for example, HCl gas or nitrous oxides and nitrogen oxides or other gases released by the decomposition of in the original one solutions existing salt are formed. These gases can be recovered. The calcination conditions are chosen that contact with oxygen is sufficient to mix from a lithium chloride salt and titanium dioxide into a lithium titanate to convert with a low level of contamination.

Depending on the ratio of the amount of lithium and titanium present, different titanates such as Li ₄ TiO ₄ , Li ₂ TiO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₃ O ₇ may be formed. Li ₄ Ti ₅ O ₁₂ spinel is the preferred form for Li insertion electrodes and is obtained by a ratio of Li to Ti (Li / Ti) of 0.116. As explained above, a slight excess of Li in the starting solution can be chosen to compensate for low losses of LiCl by evaporation.

To wash

The Calcination product may contain traces of the original lithium salt, which was used as feedstock. To the salt traces too can remove the particles are subjected to one or more washing cycles. In each cycle, the particles are mixed with water and become separated by settling or filtration. The washing step is particularly suitable when the lithium salt used is lithium chloride.

Grind or grind

After calcination and possible washing or when the lithium titanate from the in 2 or 3 selected method is prepared, the lithium titanate is suspended in water. The suspension is circulated and ground in a horizontal or vertical media mill to grind the titanate crystals to a smaller size or to equalize the size desired in the final product.

spray drying and micronizing

The product from the wet grinding process is placed in a spray dryer 45 dried at a temperature of about 120 to about 350 ° C, and preferably between about 200 to about 250 ° C. The spray-dried product can be used as a final product. Alternatively, the spray dried product can be micronized 47 and the micronized product may be the final product. Alternatively, the spray dried product can be dispersed in water or other solvent to form a dispersed slurry.

Renewed burning

Optionally, after grinding and spray drying, the lithium titanate may be re-fired in a controlled temperature furnace to produce a product having a well-controlled specific surface area consisting of regularly shaped crystals and a narrow size distribution. The re-firing temperature is selected to achieve a desired particle size and surface area of the product. In general, the re-firing temperature is between about 250 ° C and 900 ° C, and the BET surface area of the re-fired product is in the range of 1 to 400 m ² / g, with the higher re-firing temperature corresponding to the lower specific surface area. Preferably, the re-firing temperature is about 500 ° C.

According to the in 4 In the illustrated embodiment of the present invention, a lithium titanate prepared by known means is ground to a size smaller than the size desired in the final product, and is again fired to adjust the particle size to the desired level be subjected to one or more of the following steps.

dispersing or grinding

After the re-firing step, the product can be dispersed 60 In order to separate the agglomerates formed during re-firing into individual nano-sized particles (ie, release the crystallites), a water slurry of the product is formed. The dispersion can also be wet milled.

Alternatively, the product of the re-firing step may be micronized 90 , z. B. dry-milled, preferably in a jet mill.

Further processing

Depending on the destination of the final product, the product from the dispersion step may be kept as a slurry or spray dried 80 , or spray-dried 80 and micronized 90 (ie jet ground) as in 1 specified.

According to the present method, a lithium titanate having a particle size of between 5 and 2,000 nm and a BET surface area of between 1 and 200 m ² / g can be produced.

The The following examples illustrate limiting the present invention However not.

EXAMPLES

Example I

Five thousand two hundred kilograms of liquid anhydrous titanium tetrachloride was placed in a glass-lined, stirred, water-cooled reactor containing 3 m ^{3 of} a 3 M HCl solution. The maximum temperature during the injection process was 45 ° C. After the titanium-containing solution was cooled below 35 ° C, the reactor was opened and 922 kg of lithium chloride was added to form a titanium-lithium solution.

One Part of the titanium-lithium solution was further into a spray dryer introduced at a speed of 12 liters / h. The spray dryer was heated by gases, produced by the combustion of natural gas, diluted with air to to keep the temperature of the inlet gas at 600 ° C. The temperature the outlet gas was 250 ° C. The solid intermediate was placed in one at the outlet Cyclone recovered.

For the calcination step, the product recovered in the cyclone was further calcined in an oxidizing atmosphere at a temperature of 800 ° C for 12 hours. The product after calcination consisted of crystals of Li ₄ Ti ₅ O ₁₂ about 400 to about 1000 nm in size. 5 shows a scanning electron image of the product after calcination.

The product of the calcining step was further dissolved in water and ground with zirconia grinding media for 8 hours. The BET surface area of this product was 135 m ² / g.

Example II

The product of Example 1 was further spray-dried, then placed on a ceramic tray and fired in a muffle furnace at 450 ° C for 4 hours. The BET surface area of this product was 60 m ² / g.

Example III

The product of Example 1 was further spray-dried, then placed on a ceramic tray and fired in a muffle furnace at 700 ° C for 3 hours. The BET surface area of this product was 27 m ² / g. 6 shows a scanning electron image of this product.

Example IV

200 kg of an amorphous titanium compound containing 108 kg of Ti was prepared by injecting into a spray dryer of a solution of titanium oxychloride according to the method of U.S. Patent No. 09 / 503,365. The material used was the amorphous intermediate obtained after spray-drying and before the calcination step. The amorphous Ti compound was dispersed in a lithium hydroxide solution in a double-axis polyurethane-lined disperser. In total, 77.2 kg of LiOH.H ₂ O were used.

The Suspension was further introduced into a spray dryer which operated under the same conditions as the spray dryer in Example 1 has been.

The product of the spray dryer was further calcined, ground, dried and remelted at 500 ° C for 15 hours. The BET surface area of the product was 60 m ² / g.

While described what was currently considered to be preferred embodiments of the invention Experts will realize that changes and modifications performed can be without departing from the scope of the invention ent. It should all changes and modifications to be claimed within the scope of Fall invention.

Claims (27)

Process for the preparation of lithium titanate with a particle size between 5-2000 nm comprising: a) preparing a mixture comprising titanium and lithium; and b) evaporating the mixture to a mixture of Lithium titanium compounds to form, wherein the evaporation by spray drying of the mixture at a temperature above the boiling point of the liquid carried out in the mixture is, but below the temperature at which a substantial Reaction of lithium and titanium compounds occurs. The method of claim 1, wherein the mixture is calcined is to form lithium titanate. The method of claim 2, further Grasping the grinding of lithium titanate. The method of claim 2, wherein the lithium titanate is washed before it is ground. The method of claim 3, further comprising the spray drying of lithium titanate. The method of claim 5, further comprising the re-firing of the spray-dried product. The method of claim 6, wherein the re-firing at a temperature of between about 450 ° C and about 750 ° C. The method of claim 1, wherein the mixture is a aqueous solution made of titanium and lithium. The method of claim 8 wherein the lithium is a source is selected, consisting of the group of lithium chloride, lithium oxychloride, lithium nitrate, lithium hydroxide and their mixtures. The method of claim 8, wherein the solution is a Mixture of titanium oxychloride and lithium chloride. The method of claim 1, wherein the mixture is a Suspension of an amorphous oxidized titanium compound in one lithium-containing solution. The method of claim 1, wherein the evaporation process at a temperature between about 120 ° C and about 350 ° C is performed. The method of claim 2, wherein the calcining method at a temperature between about 700 ° C and about 900 ° C is performed. The method of claim 3 wherein the titanate is on a size ground which is the size of the finished one Lithium titanate product is equal to or smaller. The method of claim 1, wherein the mixture comprises a Layer of an amorphous oxidized titanium compound and a Contains lithium salt. The method of claim 15, wherein the amorphous oxidized Titanium compound is titanium dioxide and wherein the lithium salt is lithium hydroxide is. The method of claim 15, wherein the lithium salt Lithium chloride is. The method of claim 1, wherein the mixture is hollow Balls with a diameter between about 1 and 100 microns includes. The method of claim 18, wherein the hollow spheres a membrane thickness between about 30 Nanometer and 1,000 nanometers. The method of claim 1, wherein the ratio of Amount of lithium to the amount of titanium in the mixture (Li / Ti) between approximately 0.116 and 0.128. The method of claim 20, wherein the lithium titanate has a phase purity of at least 98 wt% Li ₄ Ti ₅ O ₁₂ spinel. A process for producing lithium titanate having a desired particle size between 5 and 2,000 nm and a surface area between 1 and 400 m ² / g, comprising calcining a lithium titanate having a particle size smaller than the desired size, said calcining being carried out at a temperature between about 250 ° C and about 900 ° C is performed. The method of claim 22, wherein the calcined Product is dispersed to liberate crystallites. Product according to one of claims 1 to 21. Product according to claim 24, having a particle size between 5 and 2,000 nm. The method of claim 24, having a BET surface area between 1 and 400 m ² / g. Process according to claim 25, having a BET surface area between 1 and 400 m ² / g.